Extinction

In a nutshell

The environment is constantly changing and a species will either adapt to these changes or go extinct. A species is considered extinct when there are no remaining individuals of that species still living. This may be due to the environment changing too quickly, a new predator killing a species, a new disease, or a catastrophic event such as a volcanic eruption.

Mass extinctions

Mass extinctions occur when the environment changes in a way that means organisms can't compete or reproduce. The fossil record shows five mass extinctions over geological time.

Example

Around $66\ million\ years$ ago, it is believed that a huge asteroid killed three quarters of life on Earth, including dinosaurs. The asteroid created a dust cloud that blocked the sunlight. Plants died first due to the lack of light which prevented them photosynthesising. Herbivores became extinct next and then carnivores as they relied on herbivores for their food source. Volcanic eruptions and sea level change also contributed to the extinction.

Invasive and alien species

Another cause of extinction is the introduction of a new species. The new species may be a predator of the existing species or they may compete with the existing species for food. If they are better competitors, the existing species may become extinct.

The new species could also introduce new diseases that the existing species does not have immunity against. This can cause extinction.

Example

One reason the Dodo went extinct was because of invasive species.

Example

Harlequin ladybirds are a new ladybird species in Britain. They eat other ladybirds and outcompete them for food. There is a risk that the native ladybirds may become extinct.

Sixth mass extinction

Some scientists believe that humans are currently causing a sixth mass extinction by polluting the Earth, changing the landscape and exploiting species.

Example

Bees pollinate over $70\%$ of the crop species that provide $90\%$ of the global food supply. If bees go extinct, scientists worry that humans may become extinct soon after.